I have a 1.5 year-old blue Cochin that has quit laying, comb is pale, and has lost a lot of weight (she is at 4.9 # right now). I took her to the only vet who I could find that would look at her, and they are basically clueless. She has basically quit eating (her feed anyway-she ate a cicada and some yogurt yesterday). Has anyone seen something like this before? I thought tapeworms (or worms in general), and gave her some Panacur. Any thoughts or suggestions are welcomed. Thanks!

did the vet check for coccidiosis?
It sounds like some for of parasite, coccidia, or worms. Has she had runny poop, off colored, yellow - dark brown in particular?
The wormer never hurts, need it 2-3 times a year any way. May want to try some corid in the water for her for coccidia too.
Also if rats are a problem around your area, they can carry avian tuberculosis, which will cause rapid sudden weight loss, loss of appetite and eventually death.
It's transmitted by rats getting into their feed and the chickens then eating after them. unfortunately, there is no cure if that's it. People often refer to it as "going light" cause once you realise there is a problem, they are nothing but a feathery breast bone.
More symptoms will help diagnose it.
Lack of appetite, and weight loss and pale comb can be many things, but parasites are usually on top of the list.
Good luck

Thanks for the answers. I work for the vet that I took her to (as a tech), did a fecal, absolutely nothing there. This doesn't rule out parasites, though, because sometimes things won't get picked up on a fecal exam. Her poop is normal (seems to have a lot of feathers in it, but otherwise normal). I have not seen any evidence of rats, and the other birds are showing no signs. I don't think she's egg bound, it's been over a month since she stopped laying. No mites or lice. Vent is clean. She doesn't have any sort of foul odors or discharge of any sort. I will continue with the Panacur, maybe do a blood smear tomorrow and look for abnormalities. It's very odd. She doesn't really have any other symptoms. I'm going to make her some boiled egg right now, but if anyone has any other ideas or advice, fire away!

I know that heat stress has made a few of mine pale and no appetite. One died. But there are alot of different things it could be. In fact, the other morning my silkie couldn't walk so I separated her, the next day she was fine. I'm thinking mold spores with her, since it's been so wet here. So now I got them a fan.

Do you think she might be broody or thinking about it? Or sometimes they act like that when they are going to molt.

The problem is pale and not eating is a common symptom of everything. I just try to cover all the bases that I can, and there's not much more you can do. Seems like you're doing that now. Wish for the best.

They get grit, calcium, and they range around the backyard, which is why I thought she had a tapeworm (I do have darkling beetles and other tapeworm intermediate hosts). They also get cracked corn, yogurt as a treat, and eggs.